Let say that hypothetically I issue a contract on the testnet that doesn't need to receive any ether. Kind of an ERC-20, but in this case users won't exchange real ethers for tokens. These tokens would be arbitrarily provided by the contract owner to each user. Having said that, users will also be able to transfer those tokens between them, paying the necessary gas with faucet ethers.

Under such scenario, why should I use the real network, and use real ethers if testnet can basically solve my needs?